# Does Static Friction Exist When Gravity is Applied?

• stampede247
In summary, the conversation was about whether there is static friction when an object is pulled straight against a surface by the force of gravity. The general consensus was that there is no static friction in this scenario, as the only forces acting on the object are gravity and the reaction force of the ground. Friction is only present when there is motion between the object and the surface.
stampede247
Hey guys first time posting and I have a really frustrating question. Is there static friction when the force of gravity is pulling an object straight against a surface. I believe that there is none because (i don't know if I'm wording this right) the friction is equal to the normal of the collision. Let's say you have a 20lb object on perfectly level ground. The only forces acting on the object would be gravity and the reaction force of the ground keeping the object up. Am I right about this. Looking forward to some answers. Thanks.

stampede247 said:
Let's say you have a 20lb object on perfectly level ground. The only forces acting on the object would be gravity and the reaction force of the ground keeping the object up.

Yes those will be the only two forces acting. Friction is only present when there is motion between them mass and the surface.

Thank you so much for comfirming that. I had a really long debate with a friend about this and he refused to believe it was true. Now I know how to prove it to him. Thanks for the help.

## What is static friction?

Static friction is a type of force that resists the motion of two surfaces that are in contact with each other but not moving relative to each other. It is caused by the irregularities and imperfections of the two surfaces, which create "microscopic hills and valleys" that interlock, making it difficult to move the surfaces past each other.

## How is static friction different from kinetic friction?

Static friction only occurs when two surfaces are not moving relative to each other, while kinetic friction occurs when two surfaces are in motion. Static friction is typically greater than kinetic friction, as it requires more force to overcome the interlocking of the two surfaces.

## What factors affect the magnitude of static friction?

The magnitude of static friction depends on the type of surfaces in contact, the weight of the object, and the force applied to the object. Rougher surfaces and heavier objects generally have a higher static friction, while smoother surfaces and lighter objects have a lower static friction.

## How does gravity affect static friction?

Gravity does not directly affect static friction. However, the weight of an object can indirectly affect the magnitude of static friction. As the weight of an object increases, so does the force pushing the surfaces together, resulting in a higher static friction.

## How can static friction be overcome?

Static friction can be overcome by applying a force that is greater than the force of static friction. This will cause the surfaces to start moving relative to each other, transitioning from static friction to kinetic friction. Alternatively, reducing the weight of the object or using a lubricant between the surfaces can also help reduce static friction.

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